Method and apparatus to enhance optical transparency of biological tissues

ABSTRACT

Method and apparatus for enhancing the optical transparency of biological tissue covered by a surface permeability barrier of tissue, involving the delivery of a clarifying agent to the target biological tissue to alter the attenuation characteristics of the target biological tissue.

BACKGROUND OF INVENTION

The present invention relates to modifying the optical properties oftissue on a transient basis, and more particularly, it relates to amethod and apparatus for delivery of a chemical agent to a targettissue, in order to increase the optical transmission through thistissue, on a transient basis.

It is believed that the administered chemical agent displaces theaqueous interstitial fluid of the tissue, thereby effectively alteringthe interstitial refractive index of the tissue. If the index ofrefraction of the administered chemical is closer to that of the othercomponents of the tissue, the introduction of this chemical will resultin a reduction in the heterogeneity of the refractive indices of thetissue, which in turn reduces the level of scattering within the tissue.Since optical attenuation through the tissue is primarily due toabsorption and scattering, a substantial change in scatteringdramatically affects the optical attenuation characteristics of mostbiological tissues.

Previous patents and disclosures relating to the field of this inventionhave focused on the use of a topical chemical agent for index matchingat the tissue-air interface (these prior patents and disclosures arefully identified under the heading “References” at the end of thespecifications). For instance, McCarthy, et al. (McCarthy, Fairing, &Buchholz, 1989), disclose the use of an immersion medium (such asglycerol, water, or oil) to match the refractive index of the tissuespecimen with that of an objective lens used in their confocalmicroscope. This approach serves to minimize or eliminate specularreflection, which accounts for approximately 3-4% of loss, when light isirradiated on a tissue-air interface. This approach is well known to oneskilled in the art, and Lucas, et al., disclose a similar method asearly as 1930 (Lucas, 1930).

The present invention is distinct from the prior art in that it changesthe scattering properties of biological tissues, underlying the surfacepermeability barrier of tissue covering the said biological tissue, bychanging the refractive index of the interstitial fluid within thestroma and the entire volume of the covered biological tissue. Whiletopical administration of immersion fluids affects the opticaltransmission through biological tissues by only 3-4%, the presentinvention can improve light transmission through biological tissues byup to five or six hundred percent.

The only prior art known to the inventor which teaches enhancement oftissue transparency by topical administration of chemicals is anabstract authored by Chan, et al., and the inventor, in the FourteenthAnnual Houston Conference on Biomedical Engineering Research (Chan,Nemati, Rylander, & Welch, 1996). This abstract teaches the efficacy ofthis approach for enhancing the transparency of porcine scleral tissue,in order to perform transscleral cyclophotocoagulation on glaucomatouseyes. However, this abstract does not teach bypassing of the mostsuperficial tissue layer (e.g., stratum corneum, for skin, andconjunctiva, for sclera), in order to administer the topical clarifyingagents. Without bypassing the outer-most tissue layer, the underlyingtarget tissue layers are impermeable, and the chemicals administeredtopically to the outermost tissue layer will not reach the interstitialspace of the tissue, and therefore will have no impact on the opticalproperties of the tissue. The authors indicate that a “360° peritomy wasperformed on the conjunctiva”, but peritomy alone, which is an incisionon the conjunctiva at the corneoscleral limbus of the eye, is notsufficient to allow sufficient volume of the clarifying agent to reachthe target tissue (in this case, the sclera). In order for this approachto be effective, a full surgical separation of the conjunctiva from thesclera is necessary, to allow the topical chemical agent to permeateinto the interstitial space of the sclera.

One of the objects of this invention is to provide a method andapparatus for enhancing optical transmission through biologial tissues.Other objects of this invention will become apparent from thespecifications, drawings, and by reference to the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

Referring to the drawings:

FIG. 1 illustrates the optical transmission characeristics ofdiatrizoate meglumine acid.

FIGS. 2(a), 2(b), and 2(c) illustrate the results of measurement of thediffuse transmission characteristics for porcine sclera, before andafter submersion in glycerol, after 5, 10, and 15 minutes, respectively.

FIGS. 3(a), 3(b), and 3(c) illustrate the result of measurement of thediffuse transmission characteristics for porcine sclera, before andafter submersion in diatrizoate meglumine acid, after 5, 10, and 15minutes, respectively.

FIG. 4 illustrates the absorbance of human skin, in-vivo, immediatelybefore and approximately 8 minutes after topical administration ofglycerol, over a 460 nm to 800 nm spectral range.

FIG. 5 illustrates the absorbance of human skin, in-vivo, immediatelybefore and approximately 8 minutes after topical administration ofdiatrizoate sodium injection solution (25%), over a 460 nm to 800 nmspectral range.

FIG. 6 illustrates diagrammatically a generalized system for bypassingsurface permeability barrier of tissue, administering a topicalchemical, and delivery of light.

FIG. 7 illustrates diagrammatically a suggested pattern for removing thestratum corneum.

FIG. 8 is a flowchart of a diagnostic algorithm which can be carried outin accordance with the invention.

FIG. 9 is a flowchart of a treatment algorithm which can be carried outin accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Optical transmission through biological tissue is one of the majorchallenges of all optical diagnostic and therapeutic modalities whichare intended to access structures underlying the tissue surface. Indiagnostics (e.g., imaging tissue structures with microscopes) theobjects is to obtain clear image of imbedded structures, or signatureoptical information (e.g., spectroscopic information) from analytes inthe blood stream or within the composition of biological tissues. Suchimages or optical information are distorted due to the attenuation oflight, which is transmitted through, or reflected from, the tissuespecimens.

In therapeutics (e.g., laser treatment of pigmented and vascularlesions) the goal is to selectively cause thermal necrosis in the targetstructures, without compromising the viability of surrounding tissues.The highly scattering medium of biological tissues, however, serves todiffuse the incident light, and causes thermal damage to tissuessurrounding the target structures, impacting the selectivity of theprocedure in destroying the target structures. It is therefore importantto adopt a strategy which could minimize the optical attenuation of theoverlying and surrounding tissues to treatment target structures, inorder to minimize collateral tissue damage, and maximize the therapeuticeffects at the target tissue.

When light is irradiated on biological tissues, there are severaldistinct mechanisms by which light is attenuated. The first attenuationstems from the mismatch of the index of refraction at the tissueinterface. This index mismatch results in a reflection from the tissuesurface, known as specular reflection. When the medium overlying tissueis air, this attenuation is on the order of 3-4%. Once light penetratesinto the tissue, there are two mechanisms responsible for lightattenuation: absorption and scattering. Attenuation mechanisms of tissuecan be characterized by determining the optical properties of tissue.

The optical properties of tissue provide a practical basis forcharacterizing light propagation in this medium. The fundamentalparameters which describe tissue optics are the absorption coefficient,μ_(a) (cm⁻¹), the scattering coefficient, μ_(s) (cm⁻¹), and the averagecosine of the scattering angle associated with single scattering phasefunction, g. The probability that a photon is absorbed or conservativelyscattered as it propagates in tissue, is given by the product of thepath length of the photon, Δs, and the absorption and scatteringcoefficients, respectively. The phase function describes theprobability, per unit solid angle, that a photon will be scattered intoan angle Θ. The average cosine of the phase function, g (also known asthe anisotropy factor) provides a measure of the direction ofscattering. Scattering is purely in the forward direction when g is 1 orΘ is 0°; the light is purely backscattered when g is −1, or Θ equals180°. An isotropic scattering is specified by g equaling 0.

Most of the recent advances in modeling light-tissue interaction havebeen based on the radiative transport theory. The radiative transporttheory provides a heuristic model that deals directly with the transportof power through turbid media. In this model, the distribution of lightpropagating through a turbid medium is given by the radiative transferequation (Chandrasekar, 1960): $\begin{matrix}{{s \cdot {\nabla\quad {L\left( {r,s} \right)}}} = {{{- \left( {\mu_{a} + \mu_{s}} \right)}{L\left( {r,s} \right)}} + {\mu_{s}{\int_{4\pi}{{p\left( {s,s^{\prime}} \right)}{L\left( {r,s^{\prime}} \right)}{\omega^{\prime}}}}}}} & (1)\end{matrix}$

where μ_(a) [cm⁻¹] is the absorption coefficient, μ_(s) [cm⁻¹] signifiesthe scattering coefficient p(s,s′) [sr⁻¹] is the phase functionrepresenting the contribution of scattered light from the s′ directionto s, and dω′ denotes the differential solid angle in the s′ direction.According to the radiative transport theory, the radiance L(r, s) [W m⁻²sr⁻¹] of light at position r travelling in the direction of the unitvector s is reduced due to absorption and scattering of the medium(first term on the right hand side of equation 1) and increased by thescattered contribution from s′ to s direction (second term on the righthand side of equation 1). The phase function is generally assumed to bea function only of the angle between s and s′. Thereforep(s,s′)=p(s·s′)=p (cos Θ). When the integral of the phase function isnormalized to one, p(s,s′) represents the probability density functionfor scattering from direction s′ to s.

Even though in general the phase function varies from particle toparticle, for most applications an approximate phase function is chosensuch that the most important features of the scattering process arecharacterized. In isotropic media, the phase function is simply 1/(4π).In anisotropic media (such as most biological tissues), the averagecosine of the phase function, g, is utilized to describe the degree ofanisotropy of the medium: $\begin{matrix}{g = {\int_{4\pi}{{p\left( {s \cdot s^{\prime}} \right)}\quad \left( {s \cdot s^{\prime}} \right)\quad {\omega}}}} & (2)\end{matrix}$

Scattering in a turbid medium is due to the heterogeneity of therefractive index of the constituent elements in the medium. The mainconstituent of tissue, water (by approximately 80%), has a refractiveindex of 1.33, whereas the refractive index of collagen is 1.45, and therefractive index of other constituents of tissue are also different fromwater, by a magnitude sufficient to result in a high level of opticalscattering within the tissue. Any approach which serves to minimize thisheterogeneity, will have a substantial impact on reducing the scatteringwithin the tissue, leading to a higher optical transmission through thetissue.

One approach is by applying compression. In the case of sclera, forinstance, a number of investigators have reported that when a fiberopticcontact probe is used to compress scleral tissue, the opticaltransmission through the sclera is increased. Vogel et al. (Vogel,Dlugos, Nuffer, Birngruber et al., 1991) have recently demonstrated thatthe difference in transmission diminishes with fiber contact if strongpressure is applied to the sclera. This increase in transmission due tofiber contact may be explained by the displacement of ground substancecaused by the pressure of fiber tip. The thinning of the sclera and thereduction of the distance between collagen fibrils (due to the pressureexerted by the fiber) leads to changes in the interference of the lightscattered from adjacent fibrils (Vogel et al., 1991). In this case, itis believed that more water than proteins and mucopolysaccharides aredisplaced, and that the concentration of the remaining ground substanceincreases and its refractive index becomes closer to that of thecollagen fibrils, thereby reducing the heterogeneity of the refractiveindex of the constituents of the sclera. As a result, when a contactfiber is used to compress sclera, scattering is reduced, andconsequently the transmission is increased. These effects are strongerwhen increased pressure is applied to the sclera (Cantor et al., 1989).

Another approach which has been used is the application of glycerol,topically, to enhance visualization through edematous corneas to allowadequate gonioscopic and ophthalmoscopic examinations. It has been longsince known that glycerol applied topically in concentrations from 50%to 100% is effective in clearing edematous corneas, within two minutesfollowing administration (Flood et al., 1989). It should be noted,however, that this method of applying hyperosmotic topical agents hasbeen limited only to the cornea, and the prior art does not suggest suchapplication for any other tissue type. Moreover, the method of topicaladministration of such chemical agents is ineffective in altering theoptical properties of tissues other than the cornea, so long as thesurface permeability barrier of tissue of the tissue (e.g., stratumcorneum for the skin) is in place.

The present invention involves the application of a clarifying chemicalagent to biological tissues, which are covered by a surface permeabilitybarrier of tissue, in-vivo, ex-vivo, or in-vitro, for the purpose ofaugmenting the optical transmission through these tissues. While thebasis of this effect has not been established definitively, in a numberof experiments described below, it has been shown that opticaltransmission through tissues can be substantially enhanced, on atransient basis, using the topical administration of chemicals such asdiatrizoate meglumine acid (commercially known as Hypaque®), glycerol,or glucose (hereinafter referred to as “clarifying agents”). It ispossible that the tissue transport phenomena replace a portion of thetissue's water content with the above chemical agents, and the opticalproperties of these chemicals alter the bulk optical properties of thetissue such that the optical transmission through the tissue isincreased. In time, the same transport phenomena replace these agentswith water, restoring the tissue's original optical properties.

In the case of these clarifying agents, it is possible that the higherrefractive index of these fluids (more than that of water, and closer tothe refractive index of collagen and other constituents of tissue),leads to a reduction in the heterogeneity of refractive indices of theconstituents of tissue, and therefore reduces the overall scattering oflight as it is transmitted through the tissue. This method can be termed“interstitial refractive index matching”, or IRIM.

Glycerol is a trihydric alcohol, a naturally occurring component of bodyfat. It is absorbed from the gastrointestinal tract rapidly, but at avariable rate. As such, topical administration of glycerol is notexpected to cause any adverse effects, and should be a completely safeapproach for altering the optical properties of tissues, prior to lightirradiation.

Diatrizoate meglumine acid, which is commercially known as Hypaque®, isa radiographic injection solution. In the case of Hypaque®, theincreased transmission through the tissue may be due to IRIM, or opticaltransmission characteristics which are superior to that of water, or acombination of both effects. In an experiment, a cuvette was filled withdiatrizoate meglumine acid and its optical transmission characteristicswere evaluated using a Varian CARY 5E™ UV-Vis-NIR spectrophotometer. Thetransmission characteristics were similar to that of a “high-passfilter”, and the chemical exhibited very low transmission forwavelengths below approximately 400 nm, and very high transmission forwavelengths above 400 nm (see FIG. 1).

Experiments demonstrating the effects of IRIM are described below.

Relevant Experiments

A. In-Vitro Animal Experiments

Porcine eyes were enucleated immediately post-mortem, and weretransported to the laboratory in a wet gauze pad, held at 4° C. duringtransport in a well-insulated cooler. Each eye was inflated with saline.Limbal conjunctiva and Tenon's capsule were dissected and excised usinga pair of blunt Wescott scissors. A No. 64 Beaver blade was then used tooutline 20 mm×20 mm sections of the sclera from the limbus to theequator of the globe. Incisions were deepened to the supra-choroidalspace. Sections of sclera were then lifted off the intact choroid andciliary body. Scleral thickness was measured and was determined to be1.65 mm on average.

Three prepared sections of sclera were each then placed between quartzslides, and then between two flat aluminum plates. The tissue sampleassembly was then fixed against the input port of a diffuse reflectanceaccessory (integrating sphere) of a Varian Cary 5E™ UV-Vis-NIRspectrophotometer, and diffuse transmission was measured for wavelengthsranging from 350 nm to 750 nm. The three tissue samples were thensubmerged in separate containers of glycerol, the first being submergedfor 5 minutes, the second for 10 minutes, and the third for 15 minutes.Each sample was then again placed in the tissue assembly and was fixedagainst the input port of the diffuse reflectance accessory of thespectrophotometer, and the diffuse transmission was measured again overthe same wavelength range as above. These measurements were also carriedout, using three other scleral samples, and diatrizoate meglumine acidas the IRIM agent. The results for these measurements are shown in theFIGS. 2 (a-c), and 3 (a-c).

From the results shown in FIG. 2, it can be seen that the diffusetransmission through the sclera was increased by up to 240%, 660%, and1090%, for samples which were submerged in glycerol for 5, 10, and 15minutes respectively, with the most pronounced increase occurring at 750nm wavelength (the longest wavelength for which measurements werecarried out). Similarly, the results shown in FIG. 3 illustrate that thediffuse transmission through the sclera was increased by up to 200%,395%, and 975%, for samples which were submerged in diatrizoatemeglumine acid for 5,10, and 15 minutes respectively, with the largestincrease occurring at 750 nm wavelength (the longest wavelength forwhich measurements were carried out). It is noteworthy that the samplesbecame so transparent (grossly) that when placed against print, lettersof the alphabet were clearly discernable through the tissue.

B. In-Vivo Animal Experiments

In order to assess the longitudinal effects of topical administration ofglycerol or diatrizoate meglumine acid on the sclera, in-vivoexperiments were carried out on two rabbits, and the eyes were examinedfor signs of inflammation once a day for approximately 1 week.

Each rabbit was put under anesthesia using an intra-muscular injectionof Rompin® and Ketamine®. The conjunctiva serves as the permeabilitybarrier for the sclera, and therefore, the conjunctiva was surgicallyseparated from the sclera and the distal surface of the sclera wasexposed. Topical drops of glycerol were administered on one eye, and ofdiatrizoate meglumine acid in the contra-lateral eye, for both rabbits.In the case of glycerol, the sclera turned clear, almost instantaneously(in less than 5 seconds), whereas in the case of diatrizoate meglumineacid, the sclera turned clear in approximately 1 minute. The conjunctivawas stretched over the sclera, again, and stay sutures were used tore-attach the conjunctiva to the limbal region. Ocumycin® wasadministered topically to both eyes which had undergone surgery, toprevent infection. After approximately 5-10 minutes, the sclera in botheyes became opaque, again. Follow up examination on days 1, 3, and 5showed no signs of inflammation on either eye.

C. In-Vivo Human Experiments

In order to investigate the applicability of the above method to thehuman model, and to skin tissue, additional experiments were carriedout, using topical glycerol (99.9%, Mallinckrodt, Inc.) and diatrizoatesodium injection fluid, USP, 25% (Hypaque® Sodium, 25%, by Nycomed,Inc., Princeton, N.J.).

Two skin surfaces on the forearm were shaved and cleaned prior tomeasurements. A tape-strip method was used to remove the stratumcorneum. Droplets of glycerol were then topically administered on onesite, and droplets of the diatrizoate sodium injection fluid wereadministered on the second site, which was separated from the first siteby 5 cm (a sufficient distance to ensure that the topical drugadministered on one site does not interfere with the drug administeredon the other site, through diffusion). The topical drugs administeredformed an approximate circle of 1 cm in diameter. The drugs were left todiffuse into the tissue for approximately 8 minutes.

Surface reflectance measurements were made immediately after tapestripping of the skin (prior to topical administration of the drugs),and subsequently, approximately 8 minutes after topical administrationof the drugs. A CSI Portable Diffuse Reflectance Spectrometer, developedby Canfield Scientific Instruments, Inc. (Fairfield, N.J.), was used forthese surface measurements. This device is similar in standardabsorption spectrometers, with the exception that the light source is atungsten halogen lamp, and the sample chamber is replaced with a quartzfiber optic assembly. One leg of the bifurcated fiber optic bundle iscoupled to the lamp and the other leg is coupled to the spectrometer.The joined end of the fiber bundle (approximately 3 mm in diameter) wasplaced in contact with the skin surface from which measurements weremade. The measurements were made across a 330 nm to 840 nm spectralrange, with a 0.5 nm resolution. The integration time for themeasurements was set at 50 kHz.

FIGS. 4 and 5 illustrate the results from the above measurements. Thedata displayed in these graphs have been limited to a range of 480 nm to800 nm to remove the portions of the spectra which were fraught withnoise. The tape stripping of the skin causes a mild irritation of theskin, leading to a transient erythema. This erythema was noticed in bothsites immediately after tape stripping, and subsided by the time themeasurement after topical administration of the drug was made. As such,the spectra measured prior to topical administration of the drugsclearly demonstrate the higher concentration of blood immediately belowthe surface, as evidenced by the strong oxyhemoglobin peaks atapproximately 530 nm and 560 nm.

FIGS. 4 and 5 demonstrate that the topical administration of glyceroland diatrizoate sodium injection solution, respectively, lead to anincrease in absorbance of tissue, in-vivo, of up to 60.5% and 107%respectively. This increase in tissue-absorbance is believed to becaused by IRIM, leading to a reduction of the scattering of thesuperficial layers of the skin, thereby allowing a larger percentage oflight to reach (and get absorbed by) the native chromophores of the skin(melanin and blood), thereby increasing the measured absorbance of thetissue.

It is important to note that further studies are necessary to optimizethe above experiments. For instance, the tape-stripping method forremoving the stratum corneum is generally unreliable in producingcomplete removal of this layer. Furthermore, the optimal diffusion timethrough human skin, for the above drugs, has not yet been determined. Assuch, the above experiments are only intended as a proof of principlefor the use of IRIM in increasing transparency in human tissue, in-vivo.The results, while compelling, are not intended to demonstrate the fullpotential of this powerful technique in altering the optical propertiesof human tissue.

Apparatus Concept

The apparatus of the present invention comprises the followingcomponents: a) apparatus for bypassing the surface permeability barrierof tissue, such as the stratum corneum for the skin, or the conjunctivafor the eye; b) apparatus for topically or interstitially applying achemical agent; and c) apparatus for delivery or collection of light fordiagnostic or therapeutic purposes. Since each of these componentsconsists of devices which are individually known to those skilled in theart, they are shown diagrammatically in FIG. 6. The preferred embodimentof this invention may be a combination of all three components, ordifferent combinations of the above in twos.

In order for the topical chemical agent (e.g., glycerol) to affect thetissue stroma (i.e., below the surface layer), it is necessary for thissubstance to permeate through, or bypass, the surface permeabilitybarrier of tissue. The stratum corneum is a sheet of essentially deadcells which migrate to the surface of the skin. It is well known thatdry stratum corneum is relatively impermeable to water solublesubstances, and it serves to maintain the hydration of the skin, byproviding a barrier for evaporation of the water content of the skin,and also by serving as a barrier for fluids exterior to the body todiffuse into the skin.

Therefore, in order to allow a topically administered chemical agent tobe transported into the skin, a strategy needs to be adopted to bypassthe stratum corneum. Likewise, the conjunctiva of the eye needs to bebypassed, or surgically removed, for access to the sclera; the same istrue for the epithelium of mucosal tissues. Hereinafter, this surfacetissue layer will be referred to as the “surface permeability barrier oftissue”, or SPBT, and the underlying tissue layer, as “coveredbiological tissue” or CBT.

In order to bypass the SPBT, and reach the CBT, a driving force can beapplied to move molecules across the SPBT; this driving force can beelectrical (e.g., iontophoresis, electroporation) or it may be physical,or chemical force, such as that provided by a temperature gradient, or aconcentration gradient of a clarifying agent, or of a carrier agent(carrying clarifying agent) for increasing the permeability of thesurface permeability barrier of tissue; alternatively, the driving forcemay be due to acoustic or optical pressures, as described by Weaver, etal. (Weaver, Powell, & Langer, 1991).

In the case of the stratum corneum, one configuration for component 1 ofFIG. 6 can be an electric pulse generator for inducing electroporationof the stratum corneum. This system, for instance, can be similar to theapparatus described by Prausnitz, et al.(Prausnitz et al., 1997).

Alternatively, component 1 may consist of a mechanical device withadhesive tape on the distal end, which may be brought in contact withthe skin for tape stripping the stratum corneum. With each adhesion anddetachment of the tape from the skin surface, a layer of the stratumcorneum can be removed. The component may include means of advancing thetape with each application, so that a fresh tape surface can be used ineach application.

More generally, component 1 may consist of a device which physicallybreaches the surface permeability barrier of tissue by abrasion, toexpose the underlying tissue (CBT) which has a greater permeability. Inthe case of skin, this method is commonly known as dermabrasion.

Alternatively, component 1 may be an ablative solid state laser, such asany one of the following lasers: Er:YAG, Nd:YAG, Ho:YAG, Tm:YAG,Er.YSGG, Er:Glass, or an ablative semiconductor diode laser, such as ahigh-powered GaAs laser, or an ablative excimer laser, such as an ArFlor a XeCl laser. These lasers can be used to ablate the stratum corneumin its entirety with each pulse, over the surface area covered by thelaser spot size. The short ablation depth of such lasers in human tissue(for instance, in the case of Er:YAG, an ablation depth on the order of5-10 μm) allows for a rapid removal of the stratum corneum with eachlaser pulse.

Alternatively, component 1 may be an ultrasonic generator, causingporation of the stratum corneum, for instance as described by Kost (Kostet al., 1998). This approach is sometimes referred to as sonophoresis,or phonophoresis.

In yet an alternative configuration, component 1 may be a radiofrequencygenerator, selectively ablating a finite volume of the stratum corneumwith each application, in a similar manner, for instance, as describedby Manolis et al. (Manolis, Wang, & Estes, 1994) for ablation ofarrhythmogenic cardiac tissues.

Alternatively, component 1 may be an iontophoresis system for drugdelivery through the stratum corneum, for instance as described byPrausnitz, et al. (Prausnitz et al., 1997).

Alternatively, component 1 may be a microfabricated microneedle array,long enough to cross the SPBT, but not long enough to reach the nerveendings of the tissue, as that conceived, for instance, by the needlearray developed by Henry et al. (Henry, McAllister, Allen, Prausnitz etal., 1998). The clarifying agent can be topically administered onto theSPBT and the microneedle array can then be inserted through the samesurface permeability barrier of tissue. The insertion of the needlearray will produce an array of apertures through the SPBT, which willthen cause an increase in the permeation of the clarifying agent to thecovered tissue (CBT).

Alternatively, electrical arcing may be used to ablatethe SPBT. This maybe done by an electrical generator that delivers electrical arcs at itsdelivery probe tip. Since stripping a large surface area of the stratumcorneum, for instance, may be detrimental for the viability of the skin,the openings may be formed in an array of channels, or apertures, asshown in FIG. 7.

Finally, component 1 may be a dispenser for a chemical enhancer orcarrier agent for transdermal drug delivery. In the case of the skin,for instance, it has long since been recognized that the permeability oftissue can be increased above its natural state by using penetratingsolvents, which when combined with a drug and applied to the skin,greatly increase transdermal drug delivery. An example of one suchchemical enhancer is dimethyl sulfoxide (DMSO). Other examples includedifferent alcohols such as ethanol.

In the case of the conjunctiva, it is possible to surgically separatethe conjunctiva from the sclera, prior to administration of the topicalchemical. Component 1 can consist of a device to create a surgical flapof the conjunctiva, which can subsequently be sutured back onto theintact ocular tissues. Likewise, for the epithelium of mucosa, it ispossible to use the same device to create openings in the underlyingtissue.

For both the conjunctiva and the mucosa, all of the porative approaches(e.g., electroporation, ultrasonic poration, RF poration, microneedlearray, chemical enhancement of trans-membrane delivery, oriontophoresis) may be used as component 1.

In yet another alternative configuration, the chemical may be injectedinterstitially, using an apparatus similar to a syringe with ahypodermic needle, in order to bypass the surface tissue layer. Thisapproach is more invasive, but the apparatus may be simpler.

Component 2, in FIG. 6, is an applicator for administering the chemicaltopically. One possible configuration is a syringe, which dispenses thedesired chemical over the tissue.

Finally, Component 3 of the overall system is the optical delivery orcollection apparatus, which may be a fiberoptic probe (single ormulti-fiber probe), or an articulated arm with specialized optics,depending on the optical delivery system, or optical imaging systems forimage acquisition, such as a microscope.

Applications

Since virtually all diagnostic and treatment procedures in the field ofbiomedical optics involve the probing of light into biological media,the invention described here has broad applications across a wide rangeof optical procedures. The method described here essentially serves toaugment optical penetration of biological tissues, whether fordiagnostic or therapeutic purposes.

A. Diagnostics

The present method enhances any optical method that attempts toinvestigate objects or structures imbedded, or fluids within tissues, oranalytes that exist within the blood or other biological fluids. Sincethis method serves to enhance transmission across a broad spectralrange, it can be used in routine white-light microscopy to probe atfocus planes underneath the surface. Alternatively, it could be used forspectroscopic (e.g., reflectance, fluorescence, or raman) informationgathering.

For the same reason as above, this invention can be used for confocalmicroscopy to penetrate deep into the covered tissue, CBT, (e.g., on theorder of millimeters) to examine a variety of cellular information,including cellular structures, imbedded tissue appendages, and variouspigmented and non-pigmented lesions.

Optical coherence tomography (OCT), is a diagnostic method which relieson the reconstruction of scanned interferometric information frombackscattered light from the tissue. This method is also limited in itsresolution by the extent of optical penetration through the superficiallayers, to probe imbedded objects. The present method could again serveto substantially augment the utility of OCT in investigatingobjects/structures imbedded in tissue.

Another application is the collection of fluorescence from fluorophoresimbedded in tissue, as a diagnostic means of assessing presence orabsence of biological parameters. The present method could enhance thesignal to noise ratio of such a detection scheme.

Another application is in sensing of analytes within biological fluidsin the tissue. For instance, the present invention may be used tonon-invasively measure spectrosopic information from fluids such as theblood or interstitial fluid, in order to determine glucoseconcentration, or cholesterol level.

Another application for this method is in the use of other opticalimaging methods for tumor detection, such as photon migration andoptical tomography techniques.

Another application is in the use of photodynamic means of diagnosis ofdiseased/abnormal tissues. The depth of penetration of the activatinglight generally limits photodynamic methods. The preset invention willallow deeper penetration of visible-wavelength radiation forphotodynamic activation.

FIG. 8 illustrates a typical algorithm for applying the presentinvention for a diagnostic procedure.

B. Therapeutics

The present method is applicable to a wide array of therapeutic meansinvolving imbedded objects in the tissue. In the field of ophthalmology,it encompasses all transscleral procedures, including transscleralcyclophotocoagulation, and transscleral retinopexy.

In the field of dermatology, applications include (but are not limitedto) optical (or laser) targeting of all skin appendages, including thehair follicle (for permanent laser hair removal), pigmented and vascularlesions, tattoo removal, sebaceous glands (for acne treatment),subcutaneous fat (for optical liposuction), and eccrine glands (forpermanent treatment of body odor).

The present method is applicable for photodynamic therapy of variouscancerous tissues, augmenting the delivery of light to thephotosensitizers bound to diseased tissues. As described above, thepresent invention significantly enhances the depth of penetration oflight across a broad wavelength range.

FIG. 9 illustrates a typical algorithm for applying the presentinvention to a therapeutic procedure.

Finally, the present invention also improves the efficacy of thediagnostic and therapeutic procedures, when energy sources from othersegments of the electromagnetic spectrum are used (e.g., radiofrequency,and microwaves). Since IRIM also affects the overall elastic propertiesof tissues, acoustic signals travelling through tissue could also beaffected, leading to a deeper penetration for ultrasonic waves fordiagnostic and therapeutic purposes.

From the foregoing description, it will be apparent that I have inventeda method and apparatus for enhancing optical transmission throughbiological tissues, underlying a surface permeability barrier of tissue.Variations and modifications of my invention will undoubtedly suggestthemselves to those skilled in the art and will be within the scope ofthe invention. Thus the foregoing description should be taken asillustrative, rather than in a limiting sense.

References

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I claim:
 1. Method for performing a diagnostic or therapeutic procedureon a first biological tissue having interstitial space therein andcovered by a surface permeability barrier of a second tissue, saiddiagnostic and therapeutic procedure requiring optical access into saidcovered first biological tissue, said method comprising: a) providingmeans for bypassing said surface permeability barrier of second tissueto permit the delivery of a clarifying agent past said surfacepermeability barrier of second tissue directly to said interstitialspace within said covered first biological tissue, b) delivering saidclarifying agent past said surface permeability barrier of second tissuedirectly to said interstitial space within said covered first biologicaltissue to enhance the optical transparency of said covered firstbiological tissue on a transient basis, c) performing said diagnostic ortherapeutic procedure on said covered first biological tissue while theoptical transparency thereof has been enhanced.
 2. Method as in claim 1,wherein d) said diagnostic or therapeutic application is directed ataffecting endogenous or exogenous structures or constituents within orunderlying skin.
 3. Method as in claim 2, wherein e) said endogenousstructures within skin are sebaceous glands.
 4. Method as in claim 2,wherein e) said endogenous structures within skin are hair follicles. 5.Method as in claim 2, wherein e) said endogenous structures within skinare eccrine glands.
 6. Method as in claim 2, wherein e) said therapeuticapplication is directed to affecting subcutaneous fat.
 7. Method as inclaim 2, wherein e) said therapeutic application is directed at treatingpigmented lesions of the skin.
 8. Method as in claim 2, wherein e) saiddiagnostic application is directed at treating vascular lesions of theskin.
 9. Method as in claim 2, wherein e) said diagnostic application isdirected at light microscopy of said first biological tissue.
 10. Methodas in claim 2, wherein e) said diagnostic application is directed atconfocal microscopy of said first biological tissue.
 11. Method as inclaim 2, wherein e) said diagnostic application is directed at opticalcoherence tomography of said first biological tissue.
 12. Method as inclaim 2, wherein e) said diagnostic application is directed atfluorescence spectroscopy of said first biological tissue.
 13. Method asin claim 2, wherein e) said diagnostic application is directed atreflectance spectroscopy of said first biological tissue.
 14. Method asin claim 2, wherein e) said diagnostic application is directed atnon-invasive analyte sensing.
 15. Method as in claim 2, wherein e) saiddiagnostic application is directed at measuring the glucoseconcentration in blood.
 16. Method as in claim 2, wherein e) saiddiagnostic application is directed at measuring the glucoseconcentration in interstitial fluids.
 17. Method as in claim 2, whereine) said diagnostic application is directed at measuring cholesterolconcentration in blood.
 18. Method as in claim 2, wherein e) saiddiagnostic application is directed at optical tomography of said firstbiological tissue.
 19. Method as in claim 2, wherein e) said diagnosticapplication is directed at photodynamic detection of abnormal said firstbiological tissue.
 20. Method as in claim 1, said interstitial spacehaving interstitial fluid within said said interstitial space, wherein:d) said clarifying agent alters the refractive index of saidinterstitial fluid on a transient basis to reduce the heterogeneity ofthe refractive indices within said interstitial space thereby to reducethe level of optical scaterring within said first covered biologicaltissue.